In terms of sound reduction from machinery, noise generated by industrial or commercial machinery typically comes from kinetic, combustion, or turbulence-related operations. These noises are reduced by the manufacturer either through considerate design or enclosure of the individual sources within the structure of the machine. Ventilation requirements mean that air gaps commonly exist through which sound can break-out. Silencers or mufflers can be fitted to reduce these noise pathways.
A pathway for noise transfer is the radiation of noise into the external structure or skin of the machinery, typically thin metal panels which re-radiate noise into the environment. A similar process of re-radiation of airborne or structure-borne noise occurs within some electrical equipment also contained within metallic structures. Whilst this external skin can be acoustically enhanced, unless there is a specific reason for doing so then cost, weight, and size requirements mean that typically only singular metal panels are used as an external skin on most machinery and electrical structures. As a result, remedial noise control measures need to be employed if the machinery or electrical noise is affecting a noise-sensitive receptor.
Currently employed generic methods of externally addressing mechanical or electrical parts noise include providing silencers or mufflers for ventilation noise as mentioned hereinabove; applying constrained or unconstrained damping coatings to structural panels, including the external skin of parts; complete acoustic enclosures constructed from high-mass materials such as concrete or metal, or using limp wall techniques using two thin plates separated by a viscous material for example; partially-enclosing noise barriers or walls, which may be solid, for prevention of noise transmission, or absorbent, for noise absorption; and ground/slab vibration isolation. Active noise control, by phase cancellation, may also be contemplated.
In addition to these methods, enclosures made of acoustic blankets have been used to enclose machinery to reduce noise breakout from acoustically radiating surfaces, such as metal panels, etc. Such acoustic enclosures typically have noise blocking or absorption qualities, or both.
For a flexible acoustic cover in direct contact with the noise source, different textiles, fabrics and materials are often combined to form a sound-insulating cover directly wrapped around the noise source. Such composite covers typically consist of outer protective fabric layers, typically fiberglass or canvas, and an inner absorptive layer, such as mineral wool, glass fiber, or foam for example, when attempting to reduce medium to high frequency noise. Additionally, some covers include an inner heavier mass layer, such as limp mass PVC loaded with lead or sheet steel, and then potentially a further absorptive layer for example, to reduce sound at lower frequencies. A number of companies manufacture variants on this design of acoustic cover.
Adhesives, Velcro overlaps, sewn-in cord tie-backs, quick-release clips, and/or overlapping eyelets for cord or cable-tie anchorage are mainly used for attaching acoustic blankets to a piece of equipment or machine. Alternately, a frame made of vertical posts standing from the ground and supporting horizontal cross bars is erected around the allowing and used to hang acoustic blankets.
There is still a need in the art for a method of attaching and supporting sound reduction or thermal insulation blankets to metallic machinery or structural frames.